GB1406957A - Icing detector - Google Patents

Abstract

1406957 Ice detector CANADIAN PATENTS & DEVELOPMENT Ltd 10 Oct 1973 [23 Oct 1972] 47313/73 Heading G1A In an ice detector pressurized heated air is driven via a duct 6 and plenum chamber 3 into a duct member 2 so as to entrain a secondary airflow of ambient air past an icing probe 7 positioned transversely of the duct members entrance and any ice build up formed on the probe 7 is detected by virtue of it obstructing a nearby radiation beam path from a radiation emitter 8 to a radiation sensor 9. The icing probe may comprise a central flat portion to encourage preferential ice build up near the radiation path. The ice may be removed by an electric heater designed so that the ice adjacent the ducts walls is melted before the ice at the centre of the probe. The description discloses three alternative forms of providing pressurized air into the duct member; the first Fig. 3 (not shown) deals with a series of discrete primary jets coming from the plenum chamber to direct the pressurized air into the duct member; the second Fig. 4 (not shown) provides a single jet coaxial within the duct and is fed from the plenum, and the third Figs. 5 and 6 (not shown) is similar to the Figs. 1 and 2 arrangement except that the pressurized air is directed substantially along the alls of the duct member instead of inwardly. The associated circuitry. The radiation emitter 78 is fed from a power source 75 and may be modulated. The output of the sensor 79 is amplified by an amplifier A 1 and is compared by voltage comparitors A4 & As with two reference levels provided by amplifier A2 & A 3 representing the upper and lower limits of icing, and the outputs of the voltage comparators A 4 & As are used to control a flip-flop F, which switches on and off a heater control 72 and a lamp 71. The heater control, supplies a heater 76 on the icing probe 77. Thus during operation of the system there is a continuous icing-deicing cycle, the frequency of which is directly related to the icing conditions. The amplified output of the sensor 79 is also fed via a buffer amplifier A 6 , a differentiator A 7 and a 'sample and hold' circuit to a meter 73 to indicate icing conditions. The description also discloses other similar alternative circuits Figs. 8-10 (not shown) employing logic circuitry, counters and memories.